Hall effect in the normal state of high Tc cuprates

We propose a model for explaining the dependence in temperature of the Hall effect of high T_c cuprates in the normal state, in various materials (LSCO, YBCO, BSCCO, GdBCO). They all show common features: a decrease of the Hall coefficient R_H with temperature and a universal law, when plotting R_H( T)/ R_H( T₀) versus T/ T₀ where T₀ is defined from experimental results. This behaviour is explained by using the well known electronic band structure of a CuO ₂ plane, showing saddle points at the energies E_S in the directions [0,± π] and [± π,0]. This is well confirmed by photoemission experiments. We remark that in a magnetic field, for energies E> E_S the carrier orbits are hole-like and for E< E_S they are electron-like, giving opposite contributions to R_H. We are able to fit all experimental results for a wide range of hole doping ( p_h0) (0.09< p_h0<0.30), and to fit the universal curve. For us k_BT₀ is simply E_F- E_S, where E_F is the Fermi level varying with the doping.